A memory cell of a non-volatile semiconductor storage device has a function of electrical rewriting by charge exchanges between a charge storage layer such as an insulating film having charge traps or a floating gate and a semiconductor substrate. In the memory cell, at the data writing or erasing time, since a high electric field is applied to a tunnel insulating film between the charge storage layer and the substrate to perform the change exchange, large stress is exerted on the tunnel insulating film when the writing or erasing is executed. If the writing or erasing is repetitively executed, the tunnel oxide film is deteriorated, and thus, a large number of the electron traps exist. Therefore, the control of a threshold value of the memory cell is deteriorated due to the high electric field applied at the writing or erasing time. Furthermore, the lifetime of the memory cell is shortened.